1. Field of the Invention
This invention relates to a distributed index light deflector and a method of deflecting light, and in particular, to a distributed index light deflector which has no movable mechanical parts and can be used in the blur compensation mechanisms for laser printers, bar-code readers, television cameras, and the like.
2. Background Art
Although light deflectors have been used in various equipment, most of them deflect light with mechanical movement. In laser printers, a polyhedral mirror is rotated and reflected laser beams are deflected by continuously varying the direction of the mirror. In the tracking mechanism of photomagnetic disks, light is deflected by moving a lens horizontally or by changing the direction of the reflecting mirror. A recent blur compensating mechanism for television cameras uses a prism composed of a liquid, and the image is moved on the image pickup tube by changing the shape of the prism. However, these mechanisms are complicated and are difficult to assemble and adjust, and have low resistance to vibration. In addition, the speed of deflection is limited by the size and weight of the mechanical parts. Furthermore, as the deflection speed is increased, power consumption also increases.
To solve these disadvantages, a light deflector without mechanical movement, such as a variable diffraction lattice using surface elastic wave elements (SAW device), has been proposed (see Hiroshi Sunagawa, "A Waveguide Type Acoustic Optical Wide Angle Deflector," Kogaku, Vol. 19, No. 4, p. 232). This light deflector deflects light by varying the lattice spacing by forming a SAW device in the waveguide and varying the frequency of elastic waves. However, the efficiency of diffraction is poor and the utilization of light is low, and formation of the element is difficult.
For these reasons, light deflectors utilizing liquid crystals, which allow easy fabrication of devices and allow large variations in diffraction indices, have been proposed.
These include a light deflector having an extremely large number of transparent electrodes (S. T. Kowel, D. S. Clerverly, and P. G. Kornreich, "Focusing by electrical modulation of reflection in a liquid crystal cell," Applied Opt., 23, 278 (1984)); a light deflector for deflecting light by impressing a high voltage between two electrodes to change the orientation of liquid crystals (A. F. Fray, D. Jones, "Large-angle beam deflector using liquid crystal," Electro. Lett., 11, 358 (1975)); A. Sasaki, T. Ishibashi, "Liquid-crystal light deflector," Electro. Lett., 15, 293 (1979)); a variable diffraction lattice utilizing the William's domain formed by a DC current (Mitsuharu Okano, Shunsuke Kobayashi, "Liquid Crystals: Application," Baifu-kan, p. 213 (1989)); a light deflector using switching by total reflection (G. Labrunie and S. Valette, "Nematic Liquid Crystal Digital. Light Deflector," Appl. Oct., 13, 1802 (1974)); a light deflecting device using the total reflection effect in the interface of liquid crystals (R. A. Kashnow and C. R. Stein, "Total-Reflection Liquid Crystal Electrooptic Device," Appl. Opt., 12, 2309 (1973)); Japan Society for the Promotion of Science, Committee No. 142, "Liquid Crystal Device Handbook," Nikkan Kogyo Shimbun-sha, p. 617 (1989)).
However, since the first cited light deflector described above has a large number of transparent electrodes deflect light by forming the distribution of refractive indices in a liquid crystal by controlling the voltage impressed to each electrode, the distribution of electric fields in the liquid crystal does not vary uniformly but varies stepwise. Therefore, there is a problem in that the distribution of refractive indices also becomes stepwise, resulting in disturbance of the wave surface of deflected light. Although this tendency may be decreased by increasing the number of electrodes, such a large number of electrodes would be required to maintain the smooth wave surface of the light to be deflected, that this is practically impossible.
The second cited light deflector to which a high voltage is impressed deflects light by impressing a high voltage between two separate electrodes to gradually bend liquid crystal molecules between two glass sheets. Although a large deflecting angle may be obtained in this system, there is the problem that the wave surface of the deflected light is disturbed because the distribution of refraction indices of the liquid crystal cannot be varied uniformly. The pattern of the beam is also disturbed.
The cited variable diffraction lattice utilizing William's domain forms a diffraction lattice by applying a high-voltage direct current and producing a flow of ions in the liquid crystal, and varies the size of the domain by controlling the voltage. Thus, the lattice spacing varies and the deflecting angle of the primary diffracted light is controlled. In this system, there are the problems that the intensity of higher diffracted light such as primary and secondary cannot be controlled, and the efficiency of usage of light which can be deflected is low, as in SAW devices. The deflecting angle also varies according to the wavelength of the light.
The cited light deflecting device utilizing total reflection enables deflection to be switched in only two directions, and the deflecting angle cannot be controlled continuously or randomly. Therefore, there is the problem that this system cannot be applied to laser beam scanning devices such as laser printers or to display devices.